Initiator



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Patented Dec. 17, 1935 PATENT OFFICE INITIATOB Edmund Townsend Lednum, Evanston, 11]., as-

signor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application April 29, 1333, Serial No. 668,559 4 Claims. (Cl. 102-10) This invention relates to initiators for explosives and more particularly to detonators and to shells for blasting caps and still more particularly to such shells in combination with lead azide 5 as the explosive charge.

Blasting caps as used for the detonation of high explosives comprise generally an explosive charge contained in a metal shell. Caps containing mercury fulminate as the main charge, or as the primary detonating compound, have usually had their shells constructed of the high copper alloy known as gilding metal, because of the economic advantages in its use, and because of the compatibility of mercury fulminate therewith. Copper shells, however, cannot be used when lead azide is the explosive charge, because of the highly sensitive copper azide that is formed, particularly in the presence of moisture and carbon dioxide, the formation of this sensitive copper azide making the combination hazardous. With lead azide as the cap charge, it has been customary to use shells of aluminum metal.

Initiators for high explosive shells and priming cups for small arms ammunition have likewise been commonly made of gliding metal, brass, or of alloys of copper and nickel. Pure zinc has also been suggested but it did not prove satisfactory.

While the use of aluminum shells with lead azide is satisfactory from the point of view of chemical compatibility, tliere have been objections to the use of such shells in the case of coal mine explosives, because of the excessive flash and heat on detonation, due to the high heat of combustion of aluminum. This heat is occasionally suflicient to ignite inflammable gases such as are present in gassy coal mines, with consequent hazard when this type of shell is used under such conditions.

It is an object of the invention to prepare initiators for explosives. A further object is to prepare detonators, priming cups and blasting caps which have special characteristics. A still further object is to prepare these initiators of a metal which is substantially inertto lead azide.

4 Other objects will appear hereinafter.

It has now been found that shells for initiators having unusual properties may be prepared from zinc-copper or zinc-copper-sllver alloys having a zinc content greater than 50 By way of further illustration of this invention, there are shown in the accompanying drawing three embodiments thereof applied specifically to blasting caps, in which Figures I, II and III represent respectively a fuse type blasting cap, an electric blasting cap, and a delay electric blasting cap.

- the current passing through the bridge wire H,

Figures IV, We represent a detonator for a high explosive shell, and Figures V, Va and Vb priming cups suitable for small arms ammunition. In Figures I, II and III, A represents, a shell made of my new alloy material, and B represents 5 a charge of' any suitable secondary detonating material, for example, tetryl, while 0 represents a charge of a primary detonating compound such as lead azide. D, in Figures I and III, represents an ignition material on top of the lead. azide. 10 In Figure II, E, F, G, and H represent the usual elements of an electric blasting cap, where E represents the ignition composition which is fired by which connects the cap wires G. 15 Figure In represents an electric blasting cap of the delay type, in which the delay element K is substituted for the loose charge E in Figure 11. Immediatelyafter ignition, the burning gases from the delay element escape through the opening 20 M and may be cooled by passing through the outer sleeve N. Elements F, I, J and L in Figures II and III represent a water-proofing and sealing composition.

While it has been stated in the foregoing that 25 the zinc-copper alloy used should have a zinc content of over 50% or, in other words, that the alloy should have an essentially zinc basis, it is preferable to use an alloy containing more than zinc, so that zinc is highly predominant in 30 the combination. Also, while it is essential'that some copper be alloyed with the zinc, it is preferable to have a small content of silver in addition. With the zinc present in amounts greater than 85%, the copper content should-be in ex- 35 cess of the silver content. A preferred material is an alloy of the following approximate composition:

Per cent Zinc 48.5 40 Copper 4 1'.5 Silver 1.0- 0.1

As stated above shells of pure metallic zinc have been suggested for use in the prior art. 45 Shells of such material, however, are altogether unsatisfactory, since they are soft and have little mechanical strength, and do not possess suitable working qualities. The presence of the small amounts of copper and silver in the alloy, howso ever, gives desirable hardness to the material and, at the same time, the alloy has the drawing properties such as to make it suitable for a cap shell material.

While this invention has been described with 55 be applied equally well to primers for ammunition and to detonators for high explosive shells and drop bombs, associated with a. priming chargev and with various compositions of secondary charges. In the term initiator", therefore, are included blasting caps for use with commercial high explosives of the dynamite type, detonators for high explosive shells, depth bombs, hand grenades, and the like, and primers for small arms ammunition.

It is to be understood that the foregoing 'description is illustrative only and that many other widely difierent embodiments of the invention may be practiced without departing from the spirit and scope thereof and, therefore, I do not wish to limit myself except as indicated in the appended claims.

I claim:

1. A blasting cap comprising in combination a charge of a secondary detonating compound, 9.

charge of lead azide, and a shell of a zinc-copper alloy enclosing these charges, said alloy having a zinc content greater than 50%.

2. A blasting cap comprising in combination a charge of a secondary detonating compound, a 5 charge of lead azide, and a shell of a zinc-copper alloy enclosing these charges, said alloy having a zinc content greater than 85%.

3. A blasting cap comprising in combination a charge of secondary detonating compound, a w charge of lead azlde, and a shell of zinc-coppersilver alloy containing these charges, said alloy having a zinc content greater than 85% and a copper content in excess of the silver content.

4. A blasting cap comprising in combination a 15 charge of a. secondary detonating compound, a charge of lead azide, and a shell of zinc-coppersilver alloy enclosing these charges, said alloy having the approximate compos'tion of 95-98.5% zinc, 44.5% copper, 1.0-0.1% silver. 20

EDMUND T. LFDNUM. 

